218 ANIMAL PARASITES. 



Trematoda in general, is very imperfect. Von Siebold takes 

 no particular notice of it in his ' Manual of Comparative 

 Anatomy/ (pp.. 114, 115), so that we can only cite here the general 

 remarks : " The strong membranous cutis allows a delicate, homo- 

 genous epidermis, and a tolerably firm corium, to be distin- 

 guished." Upon Distomum hepaticum, Von Siebold does not once 

 treat more at length in the notes appended to the text. From 

 the difficulty of examining this thick bodied species of Trematoda, 

 I hope that 1 shall be fairly criticised, both here and in the 

 description of the other parts of the* animal, and I only venture to 

 give what I found in an examination of this worm continued for 

 months, whilst at the same time I may remark that I have been 

 principally assisted in my investigations upon the internal struc- 

 ture of the Distoma by comparison with the work of Dr. Aubert, 

 of Breslau, upon Aspidogaster conchicola. It will be of the most 

 serviceperhaps,if, for the purpose of comparison with our Trematoda, 

 I prefix a short description of the trematode skin from Aubert. 



" That the outermost skin of the Trematoda is very thin and 

 transparent and apparently homogeneous, is best seen where it 

 forms folds, where it is torn and has turned over, where it has 

 folded itself strongly in consequence of contraction and death, 

 which also occurs most distinctly in torn fragments, or where the 

 skin is raised up from the parenchyma after long immersion in 

 water, and during, or after, the death of the animal by a sub- 

 cutaneous accumulation of water. The want of action of reagents 

 upon it is in favour of its chitinous nature. It covers the whole 

 body, and also enters into the oesophagus and genitalia, appearing 

 to cover the latter both within and without." The greater part 

 of what is here said also applies to Dlst. hepaticum. 



Although, by laying these Distoma in water for days I never 

 could detect any formation of vesicles or elevation of the epi- 

 dermis in a vesicular form, I nevertheless succeeded very well 

 occasionally in detaching separate strips of the epidermis with 

 the forceps. The structure of this skin was very finely granu- 

 lated and quite homogeneous, as was seen in places where the 

 skin was folded. Immediately after this layer follows an extremely 

 finely striated layer, in which the longitudinal fibres appear to 

 exceed the transverse ones. No pores or vacuities in the skin 

 could be detected anywhere. The hairy or spinous coat had nearly 

 fallen off from the skin of the mature Distoma, or was only still 

 to be detected on the portion between the mouth and the sucking 



